Hardface coating systems and methods for metal alloys and other materials for wear and corrosion resistant applications

ABSTRACT

The present disclosure relates generally to hardface coating systems and methods for metal alloys and other materials for wear and corrosion resistant applications. More specifically, the present disclosure relates to hardface coatings that include a network of titanium monoboride (TiB) needles or whiskers in a matrix, which are formed from titanium (Ti) and titanium diboride (TiB 2 ) precursors by reactions enabled by the inherent energy provided by the process heat associated with coating deposition and, optionally, coating post-heat treatment. These hardface coatings are pyrophoric, thereby generating further reaction energy internally, and may be applied in a functionally graded manner. The hardface coatings may be deposited in the presence of a number of fluxing agents, beta stabilizers, densification aids, diffusional aids, and multimode particle size distributions to further enhance their performance characteristics.

CROSS-REFERENCE TO RELATED APPLICATION(S)

The present disclosure is a continuation-in-part (CIP) of co-pendingU.S. patent application Ser. No. 12/122,024, filed on May 16, 2008, thecontents of which are incorporated in full by reference herein.

STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH OR DEVELOPMENT

The U.S. Government has rights to this disclosure pursuant to ContractNo. DE-AC05-00OR22800 between the U.S. Department of Energy and Babcockand Wilcox Technical Services Y-12, LLC.

FIELD OF THE DISCLOSURE

The present disclosure relates generally to hardface coating systems andmethods for metal alloys and other materials for wear and corrosionresistant applications. More specifically, the present disclosurerelates to hardface coatings that include a network of titaniummonoboride (TiB) needles or whiskers in a matrix, which are formed fromtitanium (Ti) and titanium diboride (TiB₂) precursors by reactionsenabled by the inherent energy provided by the process heat associatedwith coating deposition and, optionally, coating post-heat treatment.These hardface coatings are pyrophoric, thereby generating furtherreaction energy internally, and may be applied in a functionally gradedmanner. The hardface coatings may be deposited in the presence of anumber of fluxing agents, beta stabilizers, densification aids,diffusional aids, and multimode particle size distributions to furtherenhance their performance characteristics.

BACKGROUND OF THE DISCLOSURE

Metal alloys, such as titanium alloys and steels, are known to have agood combination of mechanical properties for many structuralapplications, but these metal alloys do not meet the wear and corrosionresistance requirements for some structural applications, such as rotorblade applications, turbine blade applications, cutting toolapplications, arc-heater applications, power generating surfaceapplications, military hardware applications, sports industry equipmentapplications (e.g., golf club heads, shoe spikes, and snow skis), moltenaluminum casting applications, and the like. Titanium alloys, forexample, have many attractive properties, such as high specific strengthand stiffness, relatively low density, and excellent corrosionresistance, but have poor resistance to wear and oxidation at hightemperatures. Conventional surfacing (such as nitriding), coatingdeposition (such as plasma spraying and sputtering), and plating havesignificant shortcomings, which include potentially providing distortedsubstrates, deteriorated surfaces, and/or weak interfacial bonding. Toovercome these shortcomings and provide high wear and corrosionresistant surfaces on metal alloy substrates, surface alloying andreactive surface modification have been developed—depositing andpost-heat treating a unique combination of materials, selected basedupon the substrate material and specific application environment.Functionally graded or layered interfaces are used to overcomeinterfacial bonding weaknesses, especially when the coefficient ofthermal expansion (CTE) is significantly different between the substrateand a ceramic or cermet surface coating.

However, what are still needed in the art are hardface coating systemsand methods for metal alloys and other materials for wear and corrosionresistant applications that overcome some of these attendantshortcomings.

BRIEF SUMMARY OF THE DISCLOSURE

In various exemplary embodiments, the present disclosure provideshardface coating systems and methods for metal alloys and othermaterials for wear and corrosion resistant applications. Morespecifically, the present disclosure provides hardface coatings thatinclude a network of titanium monoboride (TiB) needles or whiskers in amatrix, which are formed from titanium (Ti) and titanium diboride (TiB₂)precursors by reactions enabled by the inherent energy provided by theprocess heat associated with coating deposition and, optionally, coatingpost-heat treatment. These hardface coatings are pyrophoric, therebygenerating further reaction energy internally, and may be applied in afunctionally graded manner. The hardface coatings may be deposited inthe presence of a number of fluxing agents, beta stabilizers,densification aids, diffusional aids, and multimode particle sizedistributions to further enhance their performance characteristics.

Thus, the present disclosure provides a family of coatings or surfacematerials on substrate metal alloy systems for wear and corrosionresistant applications provided by deposition processes including, forexample, thermal spraying, physical vapor deposition (PVD), powdercoating followed by post-heat treatment, as well as by slurry coating.The reinforced composite structure in the coatings is preferably formedduring the thermal spray or PVD processes, whereby the process heatprovides the inherent energy to facilitate the reaction for theformation of the desired composition. In such cases, post-heat treatmentis not necessary; however, in some cases, such post-heat treatment mayincrease the percentage of reinforcement in the matrix.

Although not a primary focus of the present disclosure, surfaceengineering, surface modification, or surface alloying of the substratemetal alloys may be accomplished by depositing a slurry, suspension,blend, or mixture of selective materials onto a surface using a numberof methods, such as painting, spraying, thermal spraying, dipping,powder coating, etc., and then reactively forming the surface by heatingusing laser radiation, plasma radiation, infrared radiation, electronbeam radiation, microwave radiation, induction, welding, etc.,techniques. The surface coatings formed by this approach change thesurface characteristics of a component or structure to provideproperties of high hardness, high temperature strength, wear andcorrosion resistance, and strong adherence to the substrate, withoutsignificantly changing the bulk material properties. Layers orfunctional grading may be employed to increase bonding strength andadherence or to mitigate differences in the coefficient of thermalexpansion (CTE), whether or not post-heat treatment is utilized. Thesurface may be applied to finished components by portable fieldtechniques, or fabricated onto sheet materials prior to the finalmanufacturing steps.

The thermal spraying methods (e.g., plasma spraying, combustionspraying, wire-arc spraying, and cold spraying) and PVD methods (e.g.,cathodic arc methods, electron beam methods, evaporation methods, pulsedlaser methods, and sputtering methods) may be employed to apply thefamily of coatings of the present disclosure directly onto substratematerials with or without further high temperature heat treatment orpost-heat treatment. Additionally, since the TiB compositions of thepresent invention are pyrophoric, the inherent heat generated enhancesthe required reactions and formation and growth of the desired TiBneedles or whiskers.

In any of the above cases, the network of TiB needles or whiskers in thematrix provides a very high strength material, surpassing some of thebest ceramic materials available, especially for reinforced metal alloycomposite structures and coatings. In general, TiB is exceptionally hardand chemically inert. An important advantage of TiB over other hardceramics is that TiB may be cut by electro-discharge machining (EDM)without significant difficulty, among other advantages.

In one exemplary embodiment, the present disclosure provides a surfacetreatment for a metal alloy substrate or other material substrateproviding improved wear and corrosion resistance for a resultingcomposite structure, including: a layer of titanium and boron depositedon a surface of the substrate in the presence of sufficient depositionprocess heat such that diffusion interactions occur and the titanium andboron react to form elongate titanium monoboride structures in a matrix.The boron is deposited as titanium diboride. The matrix includestitanium. Preferably, the matrix includes β-titanium. The titanium andboron are deposited via one of a thermal spraying and physical vapordeposition technique. The titanium and boron are deposited at atemperature of between about 800 degrees C. and about 1400 degrees C.The titanium and boron are deposited in one of a substantially heatedand a substantially melted state. Optionally, the layer of titanium andboron further includes a fluxing agent selected from the groupconsisting of CaF₂, Si, and B. Optionally, the layer of titanium andboron further includes a beta stabilizer selected from the groupconsisting of molybdenum, vanadium, tantalum, niobium, manganese, iron,chromium, cobalt, nickel, copper, and silicon. Optionally, the layer oftitanium and boron further includes a densification aid selected fromthe group consisting of Fe, Mo, and an Fe alloy. Optionally, the layerof titanium and boron further includes a diffusional aid selected fromthe group consisting of CaCO₃, CaF₂, NaHCO₃, and KBF₄. Optionally, thelayer of titanium and boron comprises a plurality of particle sizes toaid diffusion interactions. Optionally, the layer of titanium and boronis deposited on the substrate in a functionally gradient manner.Optionally, the layer of titanium and boron is subjected to heattreatment subsequent to deposition on the substrate.

In another exemplary embodiment, the present disclosure provides amethod for surface treating a metal alloy substrate or other materialsubstrate to provide improved wear and corrosion resistance for aresulting composite structure, including: depositing a layer of titaniumand boron on a surface of the substrate in the presence of sufficientdeposition process heat such that diffusion interactions occur and thetitanium and boron react to form elongate titanium monoboride structuresin a matrix. The boron is deposited as titanium diboride. The matrixincludes titanium. Preferably, the matrix includes β-titanium. Thetitanium and boron are deposited via one of a thermal spraying andphysical vapor deposition technique. The titanium and boron aredeposited at a temperature of between about 800 degrees C. and about1400 degrees C. The titanium and boron are deposited in one of asubstantially heated and a substantially melted state. Optionally, thelayer of titanium and boron further includes a fluxing agent selectedfrom the group consisting of CaF₂, Si, and B. Optionally, the layer oftitanium and boron further includes a beta stabilizer selected from thegroup consisting of molybdenum, vanadium, tantalum, niobium, manganese,iron, chromium, cobalt, nickel, copper, and silicon. Optionally, thelayer of titanium and boron further includes a densification aidselected from the group consisting of Fe, Mo, and an Fe alloy.Optionally, the layer of titanium and boron further includes adiffusional aid selected from the group consisting of CaCO₃, CaF₂,NaHCO₃, and KBF₄. Optionally, the layer of titanium and boron comprisesa plurality of particle sizes to aid diffusion interactions. Optionally,the layer of titanium and boron is deposited on the substrate in afunctionally gradient manner. Optionally, the layer of titanium andboron is subjected to heat treatment subsequent to deposition on thesubstrate.

In a further exemplary embodiment, the present disclosure provides amethod for surface treating a metal alloy substrate or other materialsubstrate to provide improved wear and corrosion resistance for aresulting composite structure, including: depositing a layer of titaniumand boron on a surface of the substrate; and subsequently heating thelayer of titanium and boron such that diffusion interactions occur andthe titanium and boron react to form elongate titanium monoboridestructures in a matrix.

BRIEF DESCRIPTION OF THE DRAWINGS

The present disclosure is illustrated and described herein withreference to the various drawings, in which like reference numbers areused to denote like coating system components/method steps, asappropriate, and in which:

FIG. 1 is a schematic diagram illustrating a network of TiB needles orwhiskers in a matrix applied to the surface of a substrate, such as ametal, metal alloy, or other material, in accordance with the presentdisclosure;

FIG. 2 is a schematic diagram illustrating one exemplary embodiment of amethod for forming a coating or layer comprising a network of TiBneedles or whiskers on the surface of a substrate, such as a metal, ametal alloy, or other material, in accordance with the presentdisclosure;

FIG. 3 is a schematic diagram illustrating one exemplary embodiment of aplasma spray gun used to manufacture the coatings or layers of thepresent invention, utilizing external powder injection into a hot zoneexiting the throat area of the gun; and

FIG. 4 is a schematic diagram illustrating another exemplary embodimentof a plasma spray gun used to manufacture the coatings or layers of thepresent invention, utilizing internal powder injection prior to the hotzone exiting the throat area of the gun.

DETAILED DESCRIPTION OF THE DISCLOSURE

Again, in various exemplary embodiments, the present disclosure provideshardface coating systems and methods for metal alloys and othermaterials for wear and corrosion resistant applications. Morespecifically, the present disclosure provides hardface coatings thatinclude a network of titanium monoboride (TiB) needles or whiskers in amatrix, which are formed from titanium (Ti) and titanium diboride (TiB₂)precursors by reactions enabled by the inherent energy provided by theprocess heat associated with coating deposition and, optionally, coatingpost-heat treatment. These hardface coatings are pyrophoric, therebygenerating further reaction energy internally, and may be applied in afunctionally graded manner. The hardface coatings may be deposited inthe presence of a number of fluxing agents, beta stabilizers,densification aids, diffusional aids, and multimode particle sizedistributions to further enhance their performance characteristics. Thisnetwork of TiB needles or whiskers in a matrix 10 applied to the surfaceof a substrate 12, such as a metal alloy or other material, isillustrated conceptually in FIG. 1. The network of TiB needles orwhiskers (i.e., matrix) 10 may be applied via a thermal spray or PVDtechnique or the like, with or without post-heat treatment or the like,or via a spray or slurry coating technique or the like, with post-heattreatment or the like. In both cases, superior overall wear andcorrosion resistance is achieved. The reinforced titanium (Ti) and boron(B) materials are interjoined with the substrate 12 to provide anenhanced composite structure. The TiB needles or whiskers 10 are formedby a reactive mechanism governed by the diffusional interactions causedby either heating or melting processes: Ti+2B→TiB₂, Ti+TiB₂→2TiB.Importantly, for the purposes of this disclosure, these diffusionalinteractions are enabled by in-process heating or melting duringdeposition. Exemplary preferred temperature ranges include, but are notlimited to, 800-1350 degrees C. It should be noted that the network ofTiB needles or whiskers 10 are formed in the presence of Ti, andpreferably β-Ti.

Referring now specifically to FIG. 2, in one exemplary embodiment of thepresent disclosure, the method 14 for forming a coating comprising thenetwork of TiB needles or whiskers 10 (FIG. 1) on the surface of asubstrate 12, such as a metal, a metal alloy, or another material,includes depositing Ti and B 16 on the surface of the substrate 12,optionally via thermal spraying or PVD, such that sufficient in-processheat 18 is added to allow diffusional interactions to form the networkof TiB needles or whiskers 10. In this regard, the original Ti and B,intermediate TiB₂, and resulting TiB are in a heated or melted statewhen deposited. Optionally, post-heat treatment 20 of the depositedcoating is provided, such that the percentage of reinforcement in thematrix is increased, for example. Again, it should be noted that thenetwork of TiB needles or whiskers 10 are formed in the presence of Ti,and preferably β-Ti, and also, optionally, borides, carbides, silicides,etc. As described in greater detail herein below, the Ti and B may bedeposited in the presence of a number of fluxing agents, betastabilizers, densification aids, diffusional aids, and multimodeparticle size distributions 22 to further enhance the performancecharacteristics of the resultant network of TiB needles or whiskers 10.

Similarly, although not the primary focus of this disclosure, a strong,tough, and hard metal-ceramic composite may be formed on the surface ofthe substrate 12 by applying the Ti and B, optionally along with aself-fluxing agent and other trace components, as a slurry, paste,suspension, blend, or mixture via painting, spraying, thermal spraying,dipping, powder coating, or the like, and then heat treating using lasermeans, plasma means, electron beam means, gas torch means, electric arc(e.g., tungsten inert gas (TIG)) means, infrared means, microwave means,induction means, etc. for localized heating, in contrast to a “bulkheating” technique.

In the simplest exemplary embodiment of the present disclosure, thematerials for surfacing consist of Ti and TiB₂ in the presence of afluxing agent. The coating or alloyed surface consist of TiB in thepresence of Ti, preferably β-Ti, but may also include TiB₂, borides ofchromium, tantalum, iron, nickel, and other metal alloys, and, in somecases, carbides of these metals, and may be reactively formed ontitanium metal, steel, and other metal alloys. In some cases, silicon isadded to aid in the formation of intermetallics, and promoteself-fluxing in conjunction with B. Preferably Mo and/or Nb are added toact as stabilizers of β-Ti.

The TiB needles or whiskers 10 are formed in the matrix by a reactivemechanism which is governed by diffusional interactions either byheating or melting processes. Beta stabilizers, densification aids,diffusional aids, and multimode powder particle distributions increasethese interactions and, thus, aid in the reactive formation of the TiBneedles or whiskers 10. Molten, semi-molten, or liquid phases for one orboth of the reactive species are preferable. Processes where the molten,semi-molten, or liquid phases are inherent, such as thermal spraymethods, provide an effective vehicle for the reactive formation of theTiB needles or whiskers 10.

Again, in an alternative exemplary embodiment of the present invention,powders are blended into a slurry, applied to a substrate surface, orapplied by powder coating (as by electrostatic methods), and heated toreactively form needle-shaped TiB during growth, leading to a highaspect ratio. In other exemplary embodiments, thermal spray and/or PVDmethods are used to directly apply and form the desired compositions onthe substrates 12, to apply gradient interfaces, where appropriate, tomitigate bonding weaknesses or CTE differences and issues, and toproduce coatings from near full density to engineered porosity. In thesimplest case, the titanium-titanium monoboride (Ti—TiB) compositecoatings 10 are established, produced, and/or formed from the precursorformulations during or immediately after deposition.

The high-aspect ratio morphology is preferred to provide greaterstiffness, strength, creep resistance, and hardness. The fluxing agent,preferably an inorganic fluxing agent, is used to protect the powdersfrom oxidation, to promote homogenous melting, and to minimizesolidification defects. A number of fluxing agents may be used,including CaF₂, or B and SI, which, in conjunction, act withself-fluxing characteristics. The flux forms slag crusts after reactiveheating or melting, and, thus, no flux exists in the surface compositelayer. The heating may be accomplished by a number of differenttechniques, such as laser, electron beam, or infrared scanning acrossthe surface. The deposited slurry may be cured by heating the surface to500-1000 degrees C., depending upon the slurry carrier solvent, withsubsequent heating to melt the surface materials, thereby forming aninterface between the melted and un-melted regions. During the meltingof the surface, a large amount of hexagonal-pillar-shaped primary TiBand fine needle-shaped eutectic TiB are formed in the melted region,which is directly related to the B content. The Ti—B phase diagram showsa eutectic reaction occurring at 1540 degrees C. with a B content of1.7%. The solubility of B in Ti is nearly zero, and, thus, the TiBphases are always formed during solidification. When the B concentrationexceeds the eutectic concentration, primary TiB forms first, followed bythe formation of the eutectic TiB. Only the eutectic TiB is formed whenthe B concentration value is equal to or below 1.7%.

As used herein, the term “slurry” is used to describe a mixture having awatery consistency and including insoluble matter in a liquid. Thecarrier facilitates application of the powder to the workpiece surface.For example, the liquid carrier may consist of alcohol, a water-alcoholmixture, an alcohol-ethylacetoacetate mixture, or an alcohol-acetonemixture, to name just a few. The carrier acts as a medium for carryingor transporting the coating materials to the workpiece surface. Thecarrier is typically evaporated during the coating curing process. Thereare a number of commercially available suspension media that may beused. For example, experiments were performed using HPC, the commercialdesignation of a carrier medium manufactured by ZYP Coatings, Inc. ofOak Ridge, Tenn. This particular suspension medium consists of 98% waterand 2% Mg—Al-silicate. Surface active agents, or surfactants, such assodium lauryl sulfate, polyvinyl alcohol, and carbowax, may be added tomaintain suspension of the solid phase. Lubricants, such as stearicacid, may be added to assist in consolidation of the slurry components.Reagents to produce slurries include Klucel “G” (hydroxypropylcellulose)and polyvinylpyrrolidone (PVP).

Exemplary beta stabilizers include molybdenum, vanadium, tantalum,niobium, manganese, iron, chromium, cobalt, nickel, copper, and silicon.The beta stabilizers are subdivided into two groups: beta-isomorphous(e.g., vanadium, niobium, tantalum, molybdenum, and rhenium) andbeta-eutectoid (e.g., copper, silver, gold, palladium, indium, lead,bismuth, chromium, tungsten, manganese, iron, cobalt, nickel, uranium,hydrogen, and silicon). Vanadium, molybdenum, and niobium are the mostfrequently used beta-isomorphous forming elements in titanium-basedalloys. In general, a beta stabilizer is an alloying element that favorsthe beta crystal structure and lowers the alpha-to-beta transformationtemperatures.

As mentioned herein above, a densification aid may be added to help toincrease the density and decrease the porosity, and especially in amultimode packing of starting powder sizes. Examples of powderdensification aids are pure Fe, pure Mo, or Fe alloys, such as Fe—Mo,while the Mo and Fe—Mo can act as beta stabilizers as well. Otherdensification aids include Al, Mn, Cr, V, Ga, and alloys such as Fe—Mnand Fe—Ga. The addition of approximately 10 wt % Fe—Mo may significantlyreduce processing times. The densification aid typically has a meltingpoint below the process temperatures used for needle or whisker growth,thus, producing a liquid phase below or near the processingtemperatures. The Fe—Mo alloy is in a liquid phase around 900 degreesC., and is stable at higher temperatures.

A preferable powder is one with various sized particles for betterpacking; thus, multimode sized particles or tri-modal sized powdersprovide better packing and more contact, which aids in the diffusion andreaction of the Ti and TiB₂ and other reactive processes. As an example,using Ti powders of around 40-45 microns, typical of plasma sprayprocesses, and also 10-15 microns, along with the TiB₂ powders of around2 microns, allows moving the powders through the feeders effectively andmore optimum contact as the molten droplets are deposited onto thesubstrate.

Although TiB needle or whisker formation may occur, with good contactand diffusion, between 600 degrees C. and 1600 degrees C., a morepractical heat treatment would be between 1200 degrees C. and 1400degrees C., with a preferable temperature heat treatment range of 1250degrees C. to 1350 degrees C. Since reaction occurs by contact,diffusional aids are important and increase the mobility and diffusionof reactive atoms or molecules. Diffusional aids include calciumcarbonate, calcium fluoride, sodium bicarbonate, sodium chloride, sodiumfluoride, potassium tetrafluoroborate, potassium bicarbonate, ammoniumchloride, barium fluoride, lithium bicarbonate, or any combinationthereof, added from about 2 wt % to 40 wt %.

TiB has a high elastic modulus value (371 GPa), a CTE close to Ti(6.2×10⁻⁶/degree C and 8.2×10⁻⁶/degree C., respectively), a density of4.56 g/cc, compared to 4.5 g/cc for Ti, and may readily form as aprimary phase and/or eutectic phase during solidification processing. Moand Nb powder may be added as beta stabilizing elements. In anotherexample, the substrate may be a Ti alloy, such as Ti-6Al-4V, and thepowder blend or slurry may contain MoB powder, TiB₂ powder, and CaF₂flux. With a flux mixing ratio of 40 wt %, the melted region has a 1.1mm to 1.5 mm thick reacted surface of TiB formed homogeneously, withoutdefects. The formation of the TiB in the melted region greatly improvesthe Vickers hardness, high-temperature Vickers hardness, and the wearresistance to levels 2 to 5 times higher than those of the Ti alloysubstrate. The addition of MoB powders to the blend allows thefabrication of surface-alloyed materials with various properties bycontrolling the kind, size, and volume fraction of TiB in the surfacematrix. On Ti alloy substrates, the melted region formed by powderblends containing TiB₂ and 40 wt % CaF₂ flux or TiB₂—MoB-40CaF₂,contained hexagonal-pillar-shaped primary borides and needle-shapedeutectic borides, whereas only needle-shaped eutectic borides are foundin the MoB-40CaF₂ blends. This is directly related to the amount of B inthe melted region. The TiB₂-40CaF₂ blend provided the highest hardnessand wear resistance. The wear resistance improves as the TiB volumefraction or hardness in the melted region increases. When MoB is addedto the blend, Mo dissolved in the Ti matrix promotes β-Ti transformationsince Mo is a β-Ti stabilizer. Since β-Ti is harder than α-Ti, thepresence of Mo affects the overall hardness. Additionally, Mo provides asmoother surface important to many wear applications. Ti has a higherchemical affinity for B atoms than Mo; therefore, TiB forms instead ofMoB. The proper amount of flux prevents oxide formation by protectingthe powder melt from air, decomposing TiO₂, and precipitating boridesevenly in the melted region by the homogenous melting of boride powders.The flux does not affect the composition of the surface alloyedmaterials because no chemical reaction occurs between the flux and thesubstrate. The flux reacts with TiO₂ and H₂O to from CaO, which forms asa slag on the surface and prevents oxidation of the melted region byprotecting it from the air. It is desirable to use the smallest amountof flux possible to increase the volume fraction of boride and hardness.The resultant surface is a uniform, continuous, and crack-free coatingwith a sound and adherent interface with the metal alloy substrate, suchas Ti or steel, for example. TiB also plays a role in improvinghigh-temperature properties, since it is insoluble and chemically stableat temperatures over 1000 degrees C. On steel, the coating has acomposite nature with TiB needles and iron from the steel uniformlydistributed in the melt zone.

Although the process described above employs temperatures at or abovethe melting points of the surface, lower temperatures may be used whenthe substrate or component structure requires less heat. Surfacealloying with TiB needle formation and growth may occur in thetemperature range between 1100 degrees C. and 1300 degrees C.; however,the eutectic TiB needles require a temperature of 1540 degrees C. at alow B concentration. To obtain an alloy with high abrasive wearresistance, it must have a eutectic structure in which the hard phaseseparates out in the form of thin ramified crystals acting asmicro-reinforcement of the metallic matrix. A eutectic alloy whosemetallic matrix has the composition of steel and whose strengtheningphase is TiB₂ has, in the cast state, an abrasive wear resistance thatis several times greater than the abrasive wear resistance of steel.

Another example of a powder blend for surface alloying to form ahardfaced coating on metal alloy substrates contains TiB₂ and TiC with aflux. The reactive surface modification may be accomplished by sinteringat about 1200 degrees C. versus melting at greater than 1650 degrees C.The TiC is stable with sufficient diffusion onto the particle-titaniuminterface to create good bond strength. The TiB₂ particles react withthe Ti in-situ, transforming the particulate TiB₂ into TiB needles.

Titanium diboride (TiB₂) is a ceramic of semi-metallic nature thatreacts with Ti to form a titanium monoboride (TiB). TiB₂ has a hexagonalphase with the AlB₂ structure; whereas, the TiB formed by the reactionof Ti and TiB₂ occurs as needles embedded in excess Ti and is of the FeBtype containing B chains.

To overcome the typical shortcomings of industrial coatings and toprovide high wear and corrosion resistant surfaces on metal alloysubstrates, surface alloying or reactive surface modification has beenformed by depositing and heating a unique combination of materials,selected from the list, including boron, titanium diboride, molybdenumboride, silicon, self-fluxing materials, titanium, chromium boride,chromium, nickel, iron, molybdenum, niobium, and carbides.

Functionally graded or layered interfaces are used to overcomeinterfacial bonding weaknesses, especially when the coefficient ofthermal expansion is significantly different between the substrate andthe ceramic or cermet surface coating.

Additional examples of self-fusing alloys include self-fluxing materialsdeposited on substrates by thermal spray, slurry spray, painting, etc.,and subsequently fused using a heating process (infrared, laser,electron beam, etc.), such as self-fusing Ni—Cr alloys or self-fusingfine grade WC alloys:

Self-fusing Ni—Cr alloy with Cr, B, Fe, Si, C, Ti, balance Ni:

-   1. self-fusing Ni—Cr alloy with 10Cr, 2.7B, 2.5Fe, 2.5Si, 0.15C,    1Ti, bal Ni-   2. self-fusing Ni—Cr alloy with 10Cr, 3B, 2.5Fe, 2.5Si, 0.15C, 2Ti,    bal Ni-   3. self-fusing Ni—Cr alloy with 10Cr, 4.8B, 2.5Fe, 2.5Si, 0.15C,    10Ti, bal Ni-   4. self-fusing Ni—Cr alloy with 17Cr, 4.2Fe, 4Si, 3.5B, 1C, 1Ti, bal    Ni-   5. self-fusing Ni—Cr alloy with 17Cr, 4.5Fe, 4Si, 3.5B, 1C, 2Ti, bal    Ni

Self-fusing Ni—Cr alloy with Cr, B, Fe, Si, C, TiB2, Ti, balance Ni:

-   1. self-fusing Ni—Cr alloy with 10Cr, 3.4B, 2.5Fe, 2.5Si, 0.15C,    1TiB2, 1Ti, bal Ni-   2. self-fusing Ni—Cr alloy with 10Cr, 4.4B, 2.5Fe, 2.5Si, 0.15C,    2TiB2, 2Ti, bal Ni-   3. self-fusing Ni—Cr alloy with 10Cr, 9.4B, 2.5Fe, 2.5Si, 0.15C,    10TiB2, 10Ti, bal Ni

Self-fusing fine grade WC alloy with WC-12% Co aggregate, Ni, Cr, Fe,Si, B, C, 1Ti:

-   1. self-fusing fine grade WC alloy with WC-12% Co aggregate, 33Ni,    9Cr, 3.5Fe, 2Si, 2.2B, 0.5C, 1Ti-   2. self-fusing fine grade WC alloy with WC-12% Co aggregate, 33Ni,    9Cr, 3.5Fe, 2Si, 2.5B, 0.5C, 2Ti

Self-fusing fine grade WC alloy with WC-12% Co aggregate, Ni, Cr, Fe,Si, B, C, TiB2, Ti:

-   1. self-fusing fine grade WC alloy with WC-12% Co aggregate, 33Ni,    9Cr, 3.5Fe, 2Si, 2.9B, 0.5C, 1TiB2, 1Ti-   2. self-fusing fine grade WC alloy with WC-12% Co aggregate, 33Ni,    9Cr, 3.5Fe, 2Si, 3.9B, 0.5C, 2TiB2, 2Ti

Boride-containing Ni-base alloys are primarily composed of Ni, Cr, B,Si, and C, whereby the addition of Ti or TiB₂ provides the formation ofTiB needles. The B content typically ranges from 1.5 to 3.5% without Tiand/or TiB₂, and with increases of 0.2% B per 1% Ti and 0.7% Ti per 1%TiB₂, depending on the Cr content, which is up to about 16%. Higher Cralloys generally contain a large amount of B, which forms very hardchromium borides (˜1800 DPH); however, the addition of Ti and/or TiB₂,requires additional B. These alloys are microstructurally complex ascompared to other hardfacing alloys. Ti, Ni, Cr, B, and C determine thelevel and type of hard phase within the structure upon solidification,where B is the primary hard phase forming element for which Ti, Ni, andCr compete and C is the second hard phase former. The dominant hardphase for the boride-containing Ni-based hardfacing alloys are Ni₃B,CrB, Cr₅B₃, TiB₂, TiB, and complex carbides, M₂₃C₆ and M₇C₃ types. Theaddition of TiB₂ supplies B in the formation of TiB.

The main purpose of Si is to provide, in conjunction with B,self-fluxing characteristics. But it is also an important matrixelement, a potential promoter of intermetallic precipitates, and has amajor influence on the wear properties of the alloys. B contentinfluences the level of Si required for silicide (Ni₃Si) formation. Thehigher the B content, the lower is the Si content required to formsilicides. Boride and carbide dispersions within the microstructure leadto excellent abrasion resistance, with low stress abrasion resistancegenerally increasing with B and C contents. The boride-containingNi-based alloys possess moderate resistance to galling and are the leastresistant to corrosion of the non-ferrous hardfacing materials, due tothe lack of Cr in the matrix that follows boride and carbide formation.

The boride-containing Ni-based alloys were originally developed frombrazing alloy compositions specifically for use with the spray and fuseprocess. During the fusing process, it is believed that oxides withinthe sprayed coating combine with some of the Si and B to form aborosilicate slag which floats to the surface of the deposit. Thesealloys are used in flame spray-and-fuse coatings for applications whereexcessive wear is a problem. Parts are prepared and coated as in typicalthermal spray processes, and coatings are fused using flame or torch;induction; or in vacuum, inert, or hydrogen furnaces. These alloysgenerally fuse between 1010-1175 degrees C., which limits the substratematerials to those that can withstand this temperature range.

An example of a method to apply the reactive, surface-alloying hardfacecoating to a substrate is provided below.

After the surface alloying or coating formulation, such as theTi—TiB₂-flux formulation, is applied to the substrate or workpiece, amethod is provided for heat treating the surface coating on theworkpiece without negatively affecting the structural characteristics ofthe underlying workpiece. Initially, a workpiece is supplied with acoating. The coating is then treated using an infrared (IR) radiationhigh heat flux process. Infrared radiation rapidly heats the coatingmaterial while the temperature of the body, or core, of the workpiece ismaintained at a substantially lower temperature. From the heat deliveredby the IR process to the applied coating materials, surface alloying orreactive surface modification occurs to form the hardface coating on theselected substrate.

The heating temperature is accurately controlled by varying theintensity of the IR radiation and the time of exposure to the IRradiation source. The intensity and time of exposure are varied,depending on characteristics of the workpiece core and coatingmaterials, as well as the microstructural modification desired.Particular applications of this method may incorporate non-uniformand/or non-continuous heating profiles. A multiple-setpoint profile maybe chosen to allow various thermal treatments, such as curing orpre-heating an applied formulation to pre-cure or pre-condition beforethe final thermal treatment for forming the surface. Regardless of theprofile used, the IR intensity and exposure time may be controlled toprevent microstructural alteration of the workpiece core.

Infrared heating rapidly increases coating density, eliminating poresformed in the coating during deposition. Infrared heating also improvesthe cohesiveness of the coating material and/or the adhesion of thecoating material to the workpiece surface. In some instances, coatingadhesion to the workpiece is accomplished by partially melting theworkpiece surface to enhance diffusion of the workpiece surface into thecoating material. Other modifications or enhancements that areattainable with this method include sintering, alloying, andprecipitation. These coating modifications may, in turn, be used toperform fusing or hardening of a coating or deposit, enhance joining ofa coating to a workpiece substrate, or modify composition ormicrostructural features to achieve specific mechanical, chemical, orelectrical properties. Further, the time of exposure to IR radiationdetermines the extent of base metal dissolution into the coating.Therefore, time of exposure may be used to control both the thicknessand final composition of the coating. Non-uniform heating profiles maybe applied across a target surface area to produce coating thickness orcoating composition gradient structures. It is preferred that IR heatingbe performed in an inert atmosphere to minimize oxidation. For example,an argon-hydrogen (Ar-4% H₂) atmosphere works well.

In this embodiment of the present disclosure to form the surface alloyedmodification, a method is provided for depositing, and subsequently heattreating, a metal, ceramic, or cermet material on the surface of a metalor ceramic workpiece, or depositing a molten, semi-molten, or meltedpowder particle distribution containing the titanium, titanium diboride,and/or boron along with other additives onto the selected substrate. Thecoating material formulation is provided as a powder or a blend ofpowders. The coating powder or blend of powders is mixed with a liquidsuspension medium, which functions as a binder, facilitating applicationof the powder formulation to the workpiece surface. For someapplications, a low melting temperature metallic binder is added to thecoating mixture. The powder and suspension medium are mixed to produce ahomogeneous paint or slurry for deposition on the workpiece surface viabrush or spray-painting.

The coating is subjected to an IR radiation heating profile or tomultiple setpoint heating profiles. Upon heating, the polymericsuspension medium is burned out. In some cases, a portion of theworkpiece surface may diffuse into the coating. In some instances, thecoating material facilitates the diffusion process. For instance, whencarbon steel is coated with tungsten-carbide and then heated using IRradiation, carbon from the carbide dissolves into the steel andsignificantly lowers the melting point of the steel. For otherapplications, a low melting temperature metallic binder, such as asolder or braze alloy, is added to the coating mixture to facilitatebonding. In some cases, layers of materials or functionally gradedmaterials are used to facilitate bonding or minimize CTE mismatch.

The time of exposure to IR radiation is varied to control the extent ofbase metal dissolution into the coating, thereby controlling thethickness and final composition of the coating. Non-uniform heatingprofiles may be applied across a target surface area to produce coatingthickness or coating composition gradient structures. If flux agents arenot used, it is preferred that IR heating be performed in an inertatmosphere to minimize oxidation. For example, an argon-hydrogen (4% H₂)atmosphere works well.

A method is provided for heat treating the surface coating of aworkpiece, without negatively affecting the microstructuralcharacteristics of the underlying workpiece. The term workpiece, as usedherein, refers to a structure or body of material having a surfacecoating requiring heat treatment. For example, tools and equipment usedfor cutting and grinding often require surface coatings havingparticular characteristics, such as good hardness. The workpiece may bea metal, ceramic, polymer, composite, or some combination thereof.

The workpiece may be provided with or without a coated surface. In thelatter instance, it is necessary to initially deposit a coating. Anumber of coating deposition techniques are available. An excellentexample of a coating process is thermal spraying. Thermal spraying isadaptable to the deposition of ceramics, metals and metal alloys,polymers, composites, ceramic-metals, and multi-component, graded, ormultilayered combinations of these materials. Formation of a coatinghaving desired characteristics is accomplished by heat-treating thecoating using a high heat flux process. In this method, heat treatmentis accomplished using infrared (IR) radiation.

In contrast to commonly used coating treatments, IR radiation heatingprovides a means for rapidly heating the coating material whilemaintaining a substantially lower workpiece substrate temperature.Infrared radiation heating is preferably performed in an IR heatingfurnace. A variety of IR sources are available. For instance,tungsten-halogen based IR sources or a more powerful IR furnace,incorporating a plasma-based IR source, are available. The plasma-basedIR furnace operates as a line-focus type system, whereby the coating istreated by scanning across the coating surface.

By maintaining the workpiece temperature below a critical value, thecoating is modified while controlling the microstructure of theunderlying workpiece material. The temperature to which the coating isheated is accurately controlled by varying the intensity of IR radiationand the time of exposure to the IR radiation source. The intensity of IRradiation and time of exposure to IR radiation will vary, depending oncharacteristics of the workpiece and coating materials, and the coatingmodification or enhancement desired. For most applications, the IRexposure time ranges from 5 to 300 seconds, with an exposure time of 30to 60 seconds preferred. The preferred IR intensity, or heat fluxdensity, will generally range up to a maximum value of about 3,500Watts/cm². However, these variables are application specific and may bedeviated from. For instance, particular applications may incorporatenon-uniform and/or non-continuous heating profiles.

Infrared heating rapidly increases coating density by eliminating poresformed in the coating during deposition. IR heating is also used toimprove the cohesiveness of the coating material and/or the adhesion ofthe coating material to the workpiece surface. It may be desirable toheat a portion of the workpiece surface, in addition to heating thecoating, such that the microstructure of the heated portion of theworkpiece surface is altered. The degree to which the workpiece surfacemicrostructure is altered depends on a number of factors, including therespective workpiece and coating materials used, and the microstructuralproperties desired.

The step of IR heating may be controlled to initiate various materialmicrostructure modifying mechanisms, including sintering, alloying, andprecipitation. In the present method, sintering refers to densificationand chemical bonding of adjacent particles, which is affected by heatingto a temperature below the melting point of both the workpiece andcoating materials. Sintering may occur at the interface between thecoating and the underlying workpiece surface to improve interfacialadhesion. In addition, sintering may occur within the coating materialitself, to improve densification and mechanical strength of the coatingmaterial. The term alloying refers to heating the workpiece and coatingmaterials above their respective melting points to produce an interfacecomprising a mixture of the workpiece and coating materials. Alloying isa desirable mechanism for producing improved adhesion between thecoating and underlying workpiece surface. The term precipitationdescribes a material modification process whereby the material beingmodified, i.e., the coating and/or the workpiece surface, is heated toproduce a new solid phase that gradually precipitates within theparticular solid alloy material as a result of slow, inner chemicalreaction. This type of reaction is generally carried out to harden theparticular material.

The present method may be performed in vacuum, air, or controlled andinert environments. Infrared heating is unique in that it may be appliedto complex surface geometries with nominal effect on heating systemgeometry. Commonly used high heat flux methods require physical couplingto the coated surface, for example, with an induction coil. However,where the workpiece surface comprises an obscure geometry, a typicalinduction coil will not couple uniformly to the entire surface.Therefore, avoiding non-uniform heating of the coating surface requiresspecially designing a coil that follows the contours of the particularworkpiece. Using the instant IR heating method, the specific intensityof the thermal energy may decrease as a function of distance between theIR source and the coating surface due to dispersion of the radiation.However, in contrast to known methods, this decrease in energy isnominal. Therefore, regardless of surface geometry, the workpiececoating may be uniformly heated. The instant method provides the furtheradvantage of enabling the flexibility to heat, and thereby treat,specified portions of a surface. This flexibility is possible since theIR radiation may be directed or focused toward a particular area.

The method described herein has been successfully applied to a varietyof coatings which, historically, have proven difficult to modify. Forexample, the method may be used to uniformly flux and sinter powdercoatings over entire surface areas at a time, effectively eliminatingresidual coating porosity without heating the underlying substrate tothe sintering temperature. Although other methods have been used tosinter an entire coating surface at the same time, without heating theunderlying substrate, they typically produce inconsistent results overthe treated area. Non-uniform sintering is further exacerbated whenirregular surface geometries are being treated. In contrast, this methodis useful for effectively sintering powder coatings across workpiecesurfaces having complex geometries.

The present method has also been applied to non self-fluxing alloys. Theterm self-fluxing refers to coatings containing elements for dissolvingoxides, facilitating wetting of the coating to the underlying workpiecesubstrate. Coatings which are not self-fluxing typically must be treatedin a special atmosphere to prevent oxidation. Furthermore, the absenceof a fluxing element hinders wetting to a workpiece surface.

Aluminum alloy substrates were thermal spray coated with aluminum. Thesamples were uni-directionally heated in an IR furnace to heat thesurface coating and fuse pores formed in the coating. The workpiececoating was exposed to IR radiation, heating the coating to atemperature of 950 degrees C. for 60 seconds. This was accomplishedwithout melting the underlying aluminum substrate, using a water-cooledbacking plate, despite a substantially lower substrate melting pointtemperature of only 660 degrees C.

In another exemplary embodiment of the present disclosure, a method isprovided for depositing, and subsequently heat treating, a metal,ceramic, or combination thereof, on the surface of a metal or ceramicworkpiece. The coating material is provided in powder form. The coatingpowder may be mixed with a liquid suspension medium, or carrier, to forma slurry.

For some applications, a low melting temperature binder is added to thecoating mixture. The binder acts as a glue to hold the coating materialstogether. In some instances, the binder material, like the carrier, islost during the curing process. In other instances, the binder mayremain in the cured coating, acting as a matrix material.

The slurry may include additional components for controlling physicalcharacteristics of the slurry. For example, surface active agents, orsurfactants, such as sodium lauryl sulfate, polyvinyl alcohol, andcarbowax, may be added to maintain suspension of the solid phase.Lubricants, such as stearic acid, may be added to assist inconsolidation of the slurry components.

The slurry is deposited on a workpiece surface, preferably by brush orspray-painting. However, it will occur to one skilled in the art thatalternate deposition methods are available. For example, the workpiececould be immersed in the mixture or the slurry could be spray-dried uponthe workpiece.

Again, the time of exposure to IR radiation determines the extent ofbase metal dissolution into the coating. Therefore, time of exposure maybe used to control both the thickness and final composition of thecoating. Non-uniform heating profiles may be applied across a targetsurface area to produce coating thickness or coating compositiongradient structures. It is preferred that IR heating be performed in aninert atmosphere to minimize oxidation. For example, an argon-hydrogen(Ar-4% H₂) atmosphere works well.

For applications in which the aforementioned diffusion mechanism is notas effective, a low melting temperature metallic binder, such as asolder or braze alloy, may be added to the coating mixture. For example,a metallic matrix may be incorporated when a ceramic coating is beingapplied to a metal workpiece surface. The term low melting temperaturerefers to the fact that the metallic binder has a melting point belowthe melting point of the coating powder and the workpiece material. Uponmelting, the metallic matrix wets to the workpiece surface andwets/embodies the coating powder particles. Thus, the binder forms ametallic matrix having a hard reinforcement material formed therein.

This method has been successfully implemented to deposit a variety ofcoatings on both metal and ceramic workpiece substrates.

The thermal spray and/or PVD methods are used to directly apply and formthe desired compositions on substrates, to apply gradient interfaceswhere appropriate to mitigate bonding weaknesses or coefficient ofthermal expansion differences and issues, and to produce coatings fromnear full density to engineered porosity. In its simplest formulation,the titanium-titanium monoboride (Ti—TiB) composite coatings areestablished, produced, and/or formed from the precursor formulationsduring or immediately after deposition. During the deposition process,the inherent energy of the process heats the precursor mixture orselected formulation to the appropriate temperature between 800 degreesC. and 1300 degrees C., or higher in some cases (800 degrees C. to 1600degrees C.), resulting in the reaction and formation of TiB primary andsecondary (eutectic) phases within the Ti matrix. The TiB phases aremanifested in the Ti matrix as whiskers and/or needles. The formation ofthe TiB phases occur during the deposition and during the consolidationof the composite coating after deposition. The preferred formulationcontains approximately 18% by weight boron required to form thestoichiometric TiB composition in the Ti matrix, as shown by equations1-3:Ti+B→TiB  (1)Ti+2B→TiB₂  (2)Ti+TiB₂→2TiB  (3)

However, the Ti—TiB composite coatings may be formulated to result incoatings with a few % to more than 50% by weight TiB.

In some cases, β-stabilizers, such as Nb, Fe, Mo, Fe—Mo, orintermetallics or alloys of these and other β-stabilizers for titanium,as discussed above, are added to the precursor mixture or formulation toproduce the β-Ti matrix. In some cases, flux agents, as described above,are added and especially when the coating deposition process isperformed in atmospheric environments, typical for some thermal sprayprocesses. Vacuum plasma spraying and PVD processes typically do notrequire flux agents to mitigate oxidation from atmospheric oxygen, butmay be added to act as a flux typical of “spray-and-fuse” materials orformulations. Although the subsequent or post-heat treatment is notrequired, the resulting chemistry is still accomplished by the presenceof added Si, B, etc., containing species and compositions in thepresence of surface oxygen and any oxides.

Beta stabilizers, densification aids, diffusional aids, and multimodepowder particle distributions increase the interactions and, thus, aidin the reactive formation of the TiB whiskers. Molten, semi-molten, orliquid phases for one or both of the reactive species are morepreferable. Processes where the molten, semi-molten, or melted phasesare inherent, such as thermal spray methods, provide an effectivevehicle for the reactive formation of the TiB whiskers. Titanium powdersbetween 2 microns and 120 microns (and even greater in some cases) alongwith boron and/or titanium diboride powders between 2 microns and 15microns in diameter (and even greater in some cases) are amendable tothe thermal spray processes. However, using titanium powders around40-45 microns, typical of plasma spray processes, and also 10-15 micronsalong with the TiB₂ powders around 2 microns, allows moving the powdersthrough the feeders effectively and more optimum contact as the moltendroplets are deposited onto the substrate.

Powder is used for many thermal spray processes; however, extruded wireor cored wire containing the selective concentration of components maybe used when the thermal spray process is setup for wire feed materials.

The fluxing agent, preferably an inorganic flux, is used to protect thepowders from oxidation, to promote homogenous melting, and to minimizesolidification defects. A number of fluxing agents can be used includinga CaF₂ flux or an addition of Si and B, in conjunction, acts withself-fluxing characteristics. The flux forms slag crusts after reactiveheating or melting, and, thus, no flux exists in the surface compositelayer. The heating during the deposition and during consolidation afterdeposition is used to initiate and accomplish the action.

Thermal spraying is a group of coating processes in which finely dividedmetallic or nonmetallic materials are deposited in a molten orsemi-molten condition to form a coating. In thermal spray processes,materials are melted and propelled to the substrate with kinetic energyto build up as a coating through one or more possible bondingmechanisms; that is, mechanical bonding, diffusion, and Van der Waalsforces. The coating material may be metals, cermets, or ceramics in theform of powder, rod, wire, or molten materials. Thermal spray processesinclude combustion spraying, plasma spraying, and wire-arc spraying.

Combustion spraying uses the combination of a fuel gas and may bedivided into high velocity spraying and flame spraying depositiontechniques. During high velocity oxy-fuel (HOVF) spraying, a mixture ofgaseous fuel (such as hydrogen, methane, propane, propylene, acetylene,natural gas, etc.) or liquid fuel (such as kerosene) and oxygen is fedinto a combustion chamber, where they are ignited and combustedcontinuously. The resultant hot gas, at high pressure, travels through aconverging-diverging nozzle and then through a straight section, exitingwith a jet velocity (>1000 m/s) that exceeds the speed of sound. Apowder feed stock is injected into the gas stream, which accelerates thepowder up to 800 m/s. The stream of hot gas and powder is directedtowards the surface to be coated. The powder partially melts in thestream, and deposits upon the substrate. The resulting coating has lowporosity and high bond strength.

In flame spraying, an oxyacetylene flame (temperature ranging from 2800degrees C. to 3200 degrees C.) is used to melt the powder or wirefeedstock, which is fed into the flame through a central passage bycarrier gases, such as argon or nitrogen. The molten materials aretransported to the substrate by the mixed gases to form a coating.

Plasma spraying methods are performed in atmospheric or vacuumconditions. In a plasma spraying process, the material to be depositedis typically in the form of a powder, liquid, suspension, or wire and isintroduced into a plasma jet, emanating from a plasma spray gun ortorch. In the plasma, where the temperature is on the order of 1,000 K,the material is melted and propelled towards a substrate. The moltendroplets flatten, rapidly solidify, and form a deposit.

In wire arc spraying, two consumable metal wires are fed independentlyinto the spray gun and electrically charged to create an arc betweenthem. The heat from the arc melts the incoming wire, creating dropletsof molten materials that are entrained in an air jet from the gun. Theentrained molten feedstock deposits and builds up onto a substrate.

Physical vapor deposition (PVD) includes a variety of vacuum depositionmethods to form thin films by the condensation of a vaporized form ofthe desired film material onto substrate surfaces. Purely physicalprocesses, such as high temperature vacuum evaporation with subsequentcondensation or plasma sputter bombardment, are involved. A number ofdifferent methods are used to deposit the coating, including cathodicarc, electron beam, evaporation, pulsed laser, and sputtering (plasma,e-beam, RF, etc.). Cathodic arc deposition employs a high power electricarc discharged at the feedstock target material to blast away somematerial into highly ionized vapor that is deposited onto the substrate.In electron beam PVD, target material is heated to a high vapor pressureby electron bombardment in a vacuum, transported by diffusion, anddeposited by condensation on the substrate. During the evaporative PVDprocess, material is heated to a high vapor pressure by electricallyresistive heating in a vacuum and deposits onto a substrate. In thepulsed laser deposition process a high power laser ablates material fromthe target into a vapor that condenses and deposits onto the substrate.During sputter deposition, a glow plasma discharge, which is usuallylocalized around the “target” by a magnet, bombards and sputtersmaterial away as a vapor for subsequent deposition.

The TiB₂ precursor conversion to TiB coatings technology of the presentdisclosure provides a family of Ti—TiB composite coatings or surfacematerials that have properties of high hardness, stiffness, strength,creep-resistance, wear-resistance, corrosion-resistance, and adherence.Previously, processes to make Ti—TiB composite components, not coatings,have been reported in the literature. The goal to make the componentshas been to reinforce Ti alloys with TiB to provide improved performancerelative to specific strength, bulk modulus and stiffness, creep,corrosion resistance, wear resistance, and high temperatureapplications. The composites are Ti alloys reinforced with TiB needlesor whiskers and take advantage of the high modulus of TiB (371 GPa),coefficient of thermal expansion of TiB (6.2×10⁻⁶/degree C) close to Ti(8.2×10⁻⁶/degree C.), clean interface between Ti and TiB because of thecrystallographic relationship, formation of primary and secondaryeutectic phases during solidification, and density of TiB (4.56 g/cc)compared to Ti (4.5 g/cc).

Previously, the most common techniques reported to generate compositestructures have been combustion synthesis, rapid solidificationprocessing, and powder metallurgy that either uses commercial powders orpre-alloyed gas-atomized powders, or mechanically mixed or alloyedpowders. Following initial alloying and/or cold pressing, the compositesare usually free-sintered or hot isostatically pressed at 1300 degreesC. and a uniaxial pressure of 28 MPa in an argon atmosphere for 2 hours,which enables the densification and completes the reaction between theTi and TiB₂ powders to form the TiB whiskers inside a continuous Timatrix. The approach is based on the solid-state composite processingtemperature between 800 degrees C. and 1300 degrees C. The use of TiB asa reinforcement is attractive because there is no intermediate phasebetween the Ti and TiB, and the formation of TiB requires a far loweramount of B as compared to TiB₂.

The Ti—TiB₂ precursor composition is based on the percentage by weight,atomic percentage, or molecular content of titanium in titanium andtitanium alloys employed in the precursor composition. Pure or almostpure titanium metal (all grades) and all titanium alloys may be used asa precursor, including by weight percent, Ti-6Al-4V, Ti-24Al-10Nb(atomic %), Ti-5Al-2.5Fe, Ti-4.3Fe-7Mo-1.4Al-1.4V, Ti-6.4Fe-10.3Mo,Ti-24.3Mo, Ti-53Nb, Ti-3Al-2.5V, Ti-6Al-7Nb, Ti-4.5Al-5Mo-1.5Cr, Ti-8Mn,Ti-5Al-2Sn-2Zr-4Mo-4Cr, Ti-6Al-2Sn-4Zr-6Mo, Ti-6Al-6V-2Sn,Ti-10V-2Fe-3Al, etc., and all other Ti alloys.

Note that the powder formulations or precursor formulations may be fedinto the thermal spray gun either internally or externally, dependingupon the gun design. The reaction may initiate and form the TiB phasesand other compounds (depending upon chemistry or chemical composition)either in the hot zone of the plasma flame or during consolidation afterdeposition onto a substrate. This is illustrated in FIGS. 3 and 4.

Referring now specifically to FIG. 3, in one exemplary embodiment, theplasma spray gun 30 used to simultaneously form and apply the TiBcoatings or layers 10 (FIG. 1) of the present disclosure includes acooled cathode electrode 32 and a cooled anode electrode 34, the latterof which forms part of a nozzle 36. A high-intensity electric arc 38 isformed between the cathode electrode 32 and the anode electrode 34. Aplasma gas 40, such as Ar, Ar/He, Ar/H₂, etc., is injected through thenozzle 36, through the electric arc 38, and forms an ionized gas plasma42, which is ejected at velocity from the nozzle 36. Powder surfacingmaterials 44 are injected into the plasma 42 external to the hot zoneand nozzle 36, and are ultimately deposited onto the surface of thesubstrate 12 (FIGS. 1 and 2).

Referring now specifically to FIG. 4, in another exemplary embodiment,the plasma spray gun 30 used to simultaneously form and apply the TiBcoatings or layers 10 (FIG. 1) of the present disclosure includes acooled cathode electrode 32 and a cooled anode electrode 34, the latterof which forms part of a nozzle 36. A high-intensity electric arc 38 isformed between the cathode electrode 32 and the anode electrode 34. Aplasma gas 40, such as Ar, Ar/He, Ar/H₂, etc., is injected through thenozzle 36, through the electric arc 38, and forms an ionized gas plasma42, which is ejected at velocity from the nozzle 36. Powder surfacingmaterials 44 are injected into the plasma 42 internal to the hot zoneand nozzle 36, and are ultimately deposited onto the surface of thesubstrate 12 (FIGS. 1 and 2).

The following tables provide examples of chemical formulations (byweight %) for TiB whisker formation and reinforcement in a titaniumalloy matrix (i.e., TiBor coating) deposited onto a steel substrate,whereby a graded layer structure or a functionally gradient structuremay be formed.

TABLE 1 Updated TiBor 1 Formulations Tib Formula Tib2 (wt %) Ti (wt %)Mo (wt %) (Vol %) Vickers 1 4.99 79.73 15.27 8.44 463 2 9.58 76.44 13.9816.17 473 3 15.13 72.45 12.42 25.55 506 4 18.31 70.17 11.52 30.93 535 521.30 68.02 10.68 35.98 569 6 23.56 66.39 10.04 39.80 600 7 26.76 64.109.14 45.21 650 8 31.63 60.60 7.77 53.43 740 9 35.99 57.47 6.54 60.80 83610 39.93 54.64 5.43 67.44 935 11 43.49 52.08 4.43 73.47 1035 12 45.1550.89 3.96 76.27 1085 13 46.74 49.75 3.51 78.95 1134 14 48.25 48.66 3.0881.51 1183 15 49.71 47.62 2.67 83.96 1232 16 49.20 40.80 0 100.00 1588Graded Formulations TiBor1 Layer TiBoi/Steel TiBor Steel 4 1 75 10 4 250 50 4 3 75 25 4 100 0 5 100 0 6 100 0

Table 1 provides the simplest formulation, labeled TiBor 1 Formulations,and an example of a graded or functionally gradient structure on a steelsubstrate. To form the graded or functionally gradient structure, aselected wt % of the TiBor 1 formulation is mixed with the appropriatewt % of the steel alloy to match the substrate alloy, which is graded to100% composition of the final outer TiBor formulation.

TABLE 2 Updated TiBor 2 Formulations TiB2 Mo Tib Formula (wt %) Ti (wt%) (wt %) Si (wt %) B (wt %) (Vol %) Vickers 1 3.96 76.10 12.16 4.882.90 23.34 496 2 7.66 73.58 11.23 4.72 2.81 29.32 525 3 12.23 70.4810.08 4.52 2.69 36.68 575 4 14.89 68.67 9.41 4.41 2.62 40.96 610 5 17.4266.95 8.77 4.30 2.56 45.02 648 6 19.36 65.64 8.29 4.21 2.50 48.11 679 722.12 63.76 7.59 4.09 2.43 52.52 729 8 26.39 60.86 6.52 3.91 2.32 59.32816 9 30.29 58.21 5.54 3.74 2.22 65.50 905 10 33.87 55.78 4.64 3.58 2.1371.14 995 11 37.16 53.55 3.81 3.44 2.04 76.32 1085 12 38.70 52.50 3.423.37 2.00 78.75 1130 13 40.19 51.49 3.05 3.30 1.96 81.09 1175 14 41.6250.52 2.69 3.24 1.93 83.33 1219 15 43.00 49.58 2.34 3.18 1.89 85.49 126216 52.24 43.33 0 2.78 1.65 100.00 1588 Graded Formulation TiBor2 LayerTiBor/Steel TiBor Steel 3 1 75 10 3 2 50 50 3 3 75 25 3 100 0 4 100 0 5100 0

Table 2 expands the TiBor formulation to include B and Si. The gradedlayer or functionally gradient structure is formed as described forTiBor 1 formulation.

TABLE 3 Updated TiBor 3 Formulations TiB2 Mo Formula (wt %) Ti (wt %)(wt %) Si (wt %) B (wt %) Cr (wt %) Fe (wt %) C (wt %) 1 3.33 54.0510.23 4.11 2.44 12.22 3.06 0.56 2 6.48 62.25 9.50 4.00 2.38 11.88 2.970.54 3 10.41 60.02 8.58 3.85 2.29 11.45 2.86 0.52 4 12.73 58.71 8.043.77 2.24 11.20 2.80 0.51 5 14.95 57.45 7.53 3.69 2.19 10.96 2.74 0.50 615.65 56.48 7.13 3.52 2.16 10.78 2.69 0.49 7 19.11 55.08 6.56 3.54 2.1010.51 2.63 0.48 8 22.94 52.90 5.67 3.40 2.02 10.09 2.52 0.46 9 26.4850.89 4.84 3.27 1.94 9.71 2.43 0.44 10 29.76 49.02 4.08 3.15 1.87 9.352.34 0.43 11 32.81 47.29 3.37 3.04 1.80 9.02 2.26 0.41 12 34.26 46.473.03 2.98 1.77 8.87 2.22 0.40 13 35.65 45.68 2.71 2.93 1.74 8.72 2.180.40 14 37.00 44.91 2.39 2.88 1.71 8.57 2.14 0.39 15 38.31 44.17 2.092.83 1.69 8.43 2.11 0.38 16 47.18 39.14 0 2.51 1.49 7.47 1.87 0.34Graded Formulations TiBor3 Layer TiBor/Steel TiBor Steel 3 1 75 10 3 250 50 3 3 75 25 3 100 0 4 100 0 5 100 0

Table 3 expands the TiBor formulation to include B, Si, Cr, Fe, and C.The graded layer or functionally gradient structure is formed asdescribed for TiBor 1 formulation.

The composition of the TiBor materials or powders are pyrophoric, and,thus, being pyrotechnic heat sources, produce a large amount of heatand, typically, with little or no gases, are slow burning. The inherentheat from the pyrotechnic action may cause the formation and growthreaction or reactions to produce the TiB whiskers reinforcing thematrix.

The compositions are ideal since pyrotechnic compositions are usuallyhomogenized mixtures of small particles of fuels and oxidizers. Theparticles may be grains or flakes. Generally, the higher the surfacearea of the particles, the higher the reaction rate and burning speed.In fact, the Ti+B forms a pyrotechnic mixture, and it is one of thehottest pyrotechnic reactions available with the advantage of being asolid state gasless reaction. There must be ignition of the Ti—B mixtureto get results. Ignition may be accomplished by a number of means, suchas adding a blend of TiH₂—KClO₄ or TiH₂—NH₄ClO₄, which must be ignitedby some method like a 1 ohm bridge wire. The combustion flame sprayingshould also act as an igniter, in the thermal spray process, as well asthe welding overlay process or post-flame treatment process.

In the present disclosure, densification aids, diffusional aids, andflux agents are defined in the following manner:

-   -   Densification aids typically have a melting point below the        process temperatures used for whisker growth. Densification aids        are Fe, Mo, or Fe alloys such as Fe—Mo.    -   Diffusional aids increase the mobility and diffusion of reactive        atoms or molecules. Diffusional aids include CaCO₃, CaF₂,        NaHCO₃, KBF₄, etc.    -   Fluxing agents, such as CaF₂, Si, and B, protect the powders        from oxidation and promote homogenous melting.

However, a “pyrotechnic composition” may be added to produce asignificant amount of heat or hot particles causing heating of targetmaterial. The pyrotechnic composition contains a fuel and an oxidizer.The pyrotechnic mixtures are homogenized compositions of small particlesof fuels and oxidizers.

There are a large number of pyrotechnic compositions that could be usedin the present case:

-   -   Zr and NH₄ClO₄    -   Zr and KClO₄    -   B and KNO₃    -   Al and NH₄ClO₄    -   Al and KClO₄    -   Ti and NH₄ClO₄    -   Ti and KClO₄    -   Ti—Al and NH₄ClO₄    -   Ti—Al and KClO₄    -   ZrH₂, TiH₂, or BH and    -   NH₄ClO₄ or KClO₄    -   Ti and B (note the pyrotechnic composition)

There are many other examples of pyrotechnic compositions, including:

-   -   Fuels: metals, metal hydrides, metal carbides, non-metallic        inorganics, carbon materials, and organics;    -   Oxidizers: perchlorates, chlorates, nitrates, permanganates,        chromates, oxides, peroxides, sulfates, organics, etc.; and    -   Additives (each has a specific function): catalysts,        stabilizers, binders, etc.

Although the present disclosure has been illustrated and describedherein with reference to preferred embodiments and specific examplesthereof, it will be readily apparent to those of ordinary skill in theart that other embodiments and examples may perform similar functionsand/or achieve like results. All such equivalent embodiments andexamples are within the spirit and scope of the present disclosure, arecontemplated thereby, and are intended to be covered by the followingclaims.

What is claimed is:
 1. A method for surface treating a metal alloysubstrate or other material substrate to provide improved wear andcorrosion resistance for a resulting composite structure, comprising:depositing a layer of titanium and boron on a surface of the substratein the presence of sufficient deposition process heat such thatdiffusion interactions occur and the titanium and boron react to formelongate titanium monoboride structures in a matrix, and wherein thetitanium and boron partially diffuse into the surface of the substrateto form a reinforced material intermingled with the surface of thesubstrate to provide the composite structure; wherein one or more of thetitanium and boron are deposited at a temperature of between about 800degrees C. and 1600 degrees C.
 2. The surface treatment method of claim1, wherein the boron is deposited as titanium diboride.
 3. The surfacetreatment method of claim 1, wherein the matrix comprises titanium. 4.The surface treatment method of claim 1, wherein the matrix comprisesβ-titanium.
 5. The surface treatment method of claim 1, wherein thetitanium and boron are deposited via one of a thermal spraying andphysical vapor deposition technique.
 6. The surface treatment method ofclaim 1, wherein one or more of the titanium and boron are deposited inone of a substantially heated and a substantially melted state.
 7. Thesurface treatment method of claim 1, wherein the layer of titanium andboron further comprises a fluxing agent selected from the groupconsisting of CaF₂, Si, and B.
 8. The surface treatment method of claim1, wherein the layer of titanium and boron further comprises a betastabilizer selected from the group consisting of molybdenum, vanadium,tantalum, niobium, manganese, iron, chromium, cobalt, nickel, copper,and silicon.
 9. The surface treatment method of claim 1, wherein thelayer of titanium and boron further comprises a densification aidselected from the group consisting of Fe, Mo, and an Fe alloy.
 10. Thesurface treatment method of claim 1, wherein the layer of titanium andboron further comprises a diffusional aid selected from the groupconsisting of CaCO₃, CaF₂, NaHCO₃, and KBF₄.
 11. The surface treatmentmethod of claim 1, wherein the layer of titanium and boron comprises aplurality of particle sizes to aid diffusion interactions.
 12. Thesurface treatment method of claim 1, wherein the layer of titanium andboron is deposited on the substrate in a functionally gradient mannervia one of a thermal spraying and physical vapor deposition technique.13. The surface treatment method of claim 1, wherein the layer oftitanium and boron is subjected to heat treatment subsequent todeposition on the substrate.
 14. A method for surface treating a metalalloy substrate or other material substrate to provide improved wear andcorrosion resistance for a resulting composite structure, comprising:depositing a layer of titanium and boron on a surface of the substratein the presence of sufficient deposition process heat such thatdiffusion interactions occur and the titanium and boron react to formelongate titanium monoboride structures in a matrix, and wherein thetitanium and boron partially diffuse into the surface of the substrateto form a reinforced material intermingled with the surface of thesubstrate to provide the composite structure; wherein one or more of thetitanium and boron are deposited at a temperature of about between about800 degrees C. and 1600 degrees C.; and subsequently heat treating thelayer of titanium and boron.